After an oil or gas well bore is drilled, a well casing is generally sunk in the bore and a surface casing is "cemented in" around the well casing. The well is then ready for "completion" to prepare the well for production. In the simplest instance, well completion involves installing wellhead equipment, logging the cased well to locate the production zone(s), and perforating the casing in one or more of the production zones to put the well into hydrocarbon production. Well completion may further involve the high pressure stimulation of production zone(s) in the well to promote better production from the well.
Producing wells are sometimes "recompleted" to stimulate or prolong production. Recompletion of a well involves the perfbration of the well casing in the area of production zones where the casing was not perforated when the well was completed for initial production. Recompletion may also involve the high pressure stimulation of production zones associated with newly perforated and/or originally perforated areas of the casing. Well completion and recompletion are both generally handled by oil and gas well service providers.
The methods for drilling and casing oil and gas wells have evolved considerably in recent years, in particular, the introduction of horizontal drilling tools and techniques, as well as the exploitation of lower yield production zones have placed new demands on oil and gas well service providers responsible for completing wells for production. Traditionally, new wells have been drilled and cased and wellhead equipment has been installed as soon as the surface casing is cemented in. Consequently, any high pressure stimulation procedures required to bring the well into production are conducted using a wellhead isolation tool to protect the wellhead from the excessive pressures, abrasives and/or caustic solutions used to stimulate the flow of hydrocarbons from the production zone(s).
While this method is often effective for stimulating producing wells to increase production, it is not a cost effective way of conditioning certain new wells for production. A problem arises because wellhead isolation tools are stroked through the wellhead equipment and therefore necessarily reduce the diameter of the passage through the wellhead. If a multi-zone well requires high pressure stimulation during completion, it is necessary to initiate a multi-stage process wherein a wellhead isolation tool is stroked through the wellhead for each high pressure stimulation operation and withdrawn between stimulation operations in order to permit perforation tools, isolation plugs and/or blowout preventers, and the like to be inserted into the well. This slows the well completion process and contributes significantly to the cost of preparing a well for production. The cost is particularly significant in deep wells having horizontal bores where tool operations may take a significant amount of time. Service providers such as well fracturing and stimulation contractors charge transportation and setup fees as well as stimulation process fees. Long delays between a requirement for their service is therefore undesirable and expensive, especially if they must take down and move equipment between well stimulation processes for the same well.
To date, the only tool available to accomplish well completion in multi-zone wells requiring stimulation prior to production has been the wellhead isolation tools well known in the art.